The present invention relates to a manufacturing method of a sputtering target in which a Ta ingot or billet formed by melting and casting is subject to forging, annealing, rolling processing and the like, and to a Ta sputtering target obtained thereby.
In recent years, the sputtering method for forming a film from materials such as metal or ceramics has been used in numerous fields such as electronics, corrosion resistant materials and ornaments, catalysts, as well as in the manufacture of cutting/grinding materials and abrasion resistant materials.
Although the sputtering method itself is a well-known method in the foregoing fields, recently, particularly in the electronics field, a Ta sputtering target suitable for forming films of complex shapes and forming circuits is in demand.
Generally, this Ta target is manufactured by hot forging and annealing (heat treatment) an ingot or billet formed by performing electron beam melting and casting a Ta material, and thereafter performing rolling and finishing processing (mechanical processing, polishing, etc.) thereto. Such hot forging and annealing can be repeated. In this kind of manufacturing procedure, the hot forging performed to the ingot or billet will destroy the cast structure, disperse or eliminate the pores and segregations, and, by further annealing this, recrystallization will occur, and the precision and strength of the structure can be improved.
In this kind of manufacturing method of a target, ordinarily, recrystallization annealing is performed at a temperature of roughly 1173K (900° C.). An example of a conventional manufacturing method is described below.
Foremost, the tantalum raw material is subject to electronic beam melting and thereafter cast to prepare an ingot or billet, and subsequently subject to cold forging—recrystallization annealing at 1173K—cold forging—recrystallization annealing at 1173K—cold rolling—recrystallization annealing at 1173K—finish processing to form a target material. In this manufacturing process of a Ta target, the melted and cast ingot or billet generally has a crystal grain diameter of 50 mm or more.
As a result of subjecting the ingot or billet to hot forging and recrystallization annealing, the cast structure is destroyed, and generally even and fine (100 μm or less) crystal grains can be obtained. Nevertheless, with the conventional forging and annealing manufacturing method, there is a problem in that a pattern in the form of wrinkles or streaks is formed from the center to the peripheral edge of the disk.
FIG. 2 is a diagram showing the schematic of the target surface, and several to several ten black patterns have appeared. The micrograph of the structure of this portion of the crystal grains is shown in FIG. 3. Although there is no significant difference in the crystal grain diameter, heterophase crystal grains gathered in the form of wrinkles were observed in a part of the ordinary structure.
Generally, upon performing sputtering, finer and more uniform the crystals of the target, more even the deposition, and a film having stable characteristics with low generation of arcing and particles can be obtained.
Therefore, the existence of irregular crystal grains in the target that are generated during forging, rolling or the annealing to be performed thereafter will change the sputtering rate, and there is a problem in that evenness (uniformity) of the film will be affected, generation of arcing and particles will be promoted, and the quality of sputtered deposition may deteriorate thereby.
Further, if a forged product with stress remaining therein is used as is, the quality will deteriorate, and this must be avoided at all costs.
Accordingly, with the conventional forging and annealing process, there is a problem in that irregular crystal grains will be generated in the Ta sputtering target, and the quality of the film will deteriorate as a result thereof.